Curing Behavior and Bioepoxide Formulation From Sacha Inchi, Rubber Seed, Soybean Oils for Fabrication of Biostone as a Sustainable Alternative to Engineered Stone Using Petroleum‐Based Unsaturated polyester

ABSTRACT This study investigates the curing behaviors of four epoxidized vegetable oils, with oxirane oxygen contents ranging from 6.36% (epoxidized rubber seed oil, ERSO) to 8.78% (epoxidized sacha inchi oil, ESIO), based on their heat of curing reaction to optimize bioepoxide formulations. A constant oxirane/methylhexahydrophthalic anhydride (MHHPA) molar ratio of 1.05:1 was maintained, with 1.5 wt.% glycerol as a co‐reactant. While ESIO required 2.5 wt.% 1‐methylimidazole (NMI) as a catalyst, the other bioepoxides variants required 3.0 wt.%. The optimal curing temperatures were determined via reaction heat analysis and further validated through differential scanning calorimetry analysis (DSC), yielding peak temperatures of 120°C (ESIO), 140°C (epoxidized esterified rubber seed oil, EeRSO), and 160°C (epoxidized soybean oil, ESO). The crosslinking degree was assessed based on the residual heat of reaction from isothermally cured samples, establishing optimal processing times for engineered biostone production: 40, 50, and 60 min for ESIO, EeRSO, and the other bioepoxides, respectively. The four biostones achieved the highest performance level specified for facing materials in the European Standard EN 15285:2008 based on flexural strength, abrasion resistance, and water absorption, while satisfying selected performance criteria reported for commercial stones from Vicostone, Essastone, and Caesarstone.